Agile testing involves testing throughout the development process in short iterations to deliver working software quickly. Testers play an active role on agile teams by writing automated unit and integration tests, performing incremental functional testing, and helping ensure definitions of ready and done are met. Key aspects of agile testing include test-driven development, continuous integration, automated testing using tools like Selenium, and acceptance test-driven development approaches like behavior-driven development. Potential issues testers may face include insufficient estimation, time constraints, and silos between teams.